Various heat generating devices having a heat generating material sealed in an air-permeable flat bag which are used to warm a human body by the heat generated by the heat generating material are known. The heat generating device has an adhesive applied to the outer side thereof so that the device may be attached to a body or clothing of a wearer. When a heat generating device of this type is attached to a movable part of a wearer's body, such as a joint, it is likely that the heat generating device fails to sufficiently conform to the movement of the part, which can cause the adhesive to separate from the adherend or cause uncomfortable skin tightness to the wearer.
To avoid this, a stretch member can be used in heat generating device. For example, Patent Document 1 discloses a disposable body warmer attached to a stretch member or a plurality of disposable body warmers connected as wrapped in a stretch member so that the disposable body warmer may have a good fit against a human body. Patent Document 2 discloses a stretchable heat generating device having a bag formed of a stretch material and a heat generating element sealed in the bag. The assignee of the present invention has proposed a warming device having a heat generating portion having a plurality of heat generating parts, in which the heat generating portion includes a stretch part so that the heat generating portion may stretch between every heat generating parts (see Patent Document 3). However, any of the above described devices has a limited stretchable portion because the stretch part is only formed between heat generating parts or elements. Moreover, when a stretch member directly covers a heat generating element, the stretch of the stretch member is hindered. Therefore, the warming devices described in these patent documents are, while stretchable, not always sufficiently follow the movement of a moving part of a wearer.    Patent Document 1 JP 6-61222U    Patent Document 2 JP 2006-51191A    Patent Document 3 JP 2000-139992A